1. Field of the Invention
The present invention relates to a method of fabricating a solar cell, and more particularly, to a method of fabricating a solar cell with low costs and favorable process controllability.
2. Description of Related Art
Solar energy is a kind of clean, non-pollutant and inexhaustible energy resource. Since the pollution and supply shortage problem resulted from petrochemical energy resource, solar energy frequently draws attention. Because solar energy can be converted into electric power by solar cells directly, research and development of solar cells become an important issue.
Silicon-based solar cell is a well-known solar cell. In the silicon-based solar cell, a P-N junction is generated between different types of semiconductor layers (i.e. P-type semiconductor layer and N-type semiconductor layer). When the P-N junction is irradiated by sunlight, electron-hole pairs are generated because electrons in the semiconductors are excited from a valence band into a conductive band by transferring the energy of photons. Electrons and holes are affected by an electric field such that holes move along the direction of the electric field and electrons move along a direction opposite to the direction of the electric field. When the solar cells are electrically coupled to a load via connection wires, a loop is formed and a current generated from the solar cells flows through the load.
In the solar cells, an N+ doping region is required to be formed between a contact conductor and a N-type semiconductor layer such that an ohmic contact between the contact conductor and the N-type semiconductor layer is formed. In the prior arts, the N+ doping region is fabricated by photolithography process, laser patterning process or etch-back process. Obviously, fabrication of the N+ doping region requires additional process, and fabrication costs of solar cells increases due to the fabrication of the N+ doping region. Moreover, the photolithography process, laser patterning process or etch-back process for fabricating the N+ doping region is difficult to control. During the photolithography process, laser patterning process or etch-back process, defects in the semiconductor layer often generate and yield-rate of the solar cells decreases accordingly. How to increase yield-rate of the solar cells without significantly increasing fabrication costs is a problem to be solved.